Parallel rule

ABSTRACT

A parallel rule is disclosed having two component rules ( 4, 6 ) each providing one of two opposed parallel straight edges. A linkage ( 10 ) allows relative movement of the rules in a direction orthogonal to the straight edges but prohibits relative movement in a direction parallel to the straight edges. At least one component rule has at least one through hole ( 12 )suitable to receive the point of a pencil.

This invention relates to parallel rules.

Parallel rules are used for navigation purposes to transfer a directionfrom one position to another on a chart. Thus a direction may be takenfrom a compass rose marked on the chart and drawn through a particularposition on the chart so as to indicate a course or a transit, forexample. When using navigational aids such as sextants or electronicglobal positioning systems (GPS) it is also necessary to mark a positionwhere a line of latitude intersects a line of longitude, so as to showthe craft's position.

Against this background, in accordance with one aspect of the invention,there is provided a parallel rule, comprising two component rules eachproviding one of two opposed parallel straight edges, and a linkageallowing relative movement of the rules in a direction orthogonal to thestraight edges but prohibiting relative movement in a direction parallelto the straight edges, wherein at least one component rule has at leastone through hole suitable to receive the point of a pencil.

Such a rule may be used conventionally to mark a line of longitudethrough a particular easting or westing by placing one straight edgeparallel to a line of longitude shown on the chart and expanding therule until one or other straight edge crosses the particular easting orwesting indicated at the edge of the chart. The rule may then be used tomark a northing by placing an edge adjacent the northing scale at theedge of the chart, so that the or a hole is positioned at the requirednorthing, placing the point of a pencil in the hole and expanding therule to draw a line of latitude on the chart at the required northing.In the alternative the line of longitude could be drawn analogously.

Most preferably, both component rules have through holes incorresponding positions. This allows one hole to be lined up with theappropriate northing and the pencil point to be inserted in thecorresponding hole on the other component rule.

In one form the linkage may comprise an intermediate member connected toeach component rule by a respective set of three links, two links ineach set being pivotally connected to both the intermediate member andthe component rule by pivots situated on corners of a variableparallelogram, the other link in each set being pivotally connected tothe component rule and both pivotally and slidably connected to theintermediate member for sliding movement together, parallel to thestraight edges.

In another form the linkage may comprise two links each pivotallyconnected to a respective component rule, each pivotally and slidablyconnected to the other component rule for sliding movement parallel toits straight edge and pivotally connected together between the componentrules.

Another aspect of the invention extends to a parallel rule, comprisingtwo component rules each providing one of two opposed parallel straightedges, and a linkage allowing relative movement of the rules in adirection orthogonal to the straight edges but prohibiting relativemovement in a direction parallel to the straight edges, the parallelrule being contained by a package, the package being so formed that atleast part of the parallel rule is visible therethrough, and so that thecomponent rules may be opened and closed. This allows a prospectivepurchaser to operate the rule without removing it from its package.

In yet another aspect, the invention provides a parallel rule having twocomponent rules so linked as to constrain them to remain parallel,wherein both component rules are provided on their undersides with apair of spaced bosses, the bosses being of relatively low frictionmaterial, and between the bosses with at least one area of relativelyhigh friction material, the bosses projecting further from the componentrules than the high friction areas. As the component rules will beinherently a little flexible, pressing a component rule between thebosses, brings the relatively high friction material into contact with,say, a chart, firmly locating the rule thereon. Releasing the pressureraises the relatively high friction area from the chart so allowing thecomponent rule to glide over the chart on the relatively low frictionbosses. One component rule may thus be firmly located while the other isadjusted to its desired position.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a parallel rule embodying the invention, whenclosed;

FIG. 2 is a cross sectional view of the rule of FIG. 1;

FIG. 3A is a plan view of the rule of FIG. 1 shown in an open position;

FIG. 3B is a pictorial detail of an alternative arrangement to that ofFIG. 1;

FIG. 4 is a plan view of another parallel rule embodying the invention,shown in its closed position;

FIG. 5 shows the parallel rule of FIG. 4 in an open position;

FIG. 6 is a pictorial view of the rule of FIG. 1 in a package; and

FIG. 7 is a side view of the parallel rules of FIGS. 1 to 5.

Referring to the drawings, the parallel rule 2 has two component rules 4and 6. Each component rule 4 or 6 has a straight bevelled edge 8positioned so that the straight edges are opposed and on the outside ofthe parallel rule. The component rules 4 and 6 are connected by alinkage 10 which allows relative movement of the rules in a directionorthogonal to the straight edges but prohibits relative movement in adirection parallel to the straight edges.

In each component rule 4 and 6, behind and proximate each straight edge8, in the bevel thereof, are conveniently positioned a plurality ofthrough holes 12 suitable to receive the point of a pencil. The holes 12have a diameter of from 0.5 mm to 3 mm diameter, preferably 2 mmdiameter, at the underside of the component rules. The holes arecylindrical for about 1 mm and open out at an included angle of about60° towards the upper surface of the component rules where theirdiameters are about 4 mm. The holes 12 are placed in correspondingpositions along each straight edge. In use, for example, the straightedge 8 of component rule 4 is aligned with a line of longitude at theedge of a chart so that one of the holes 12 covers a desired mark on thenorthing scale. A pencil point is put in the corresponding hole 12 inthe other component rule 6. Holding the component rule 4 still, thepencil and component rule 6 are moved to mark the chart with what is aline of latitude passing through the desired northing. The rule can beused conventionally or in a similar fashion to mark an intersecting lineof longitude passing through a desired easting or westing, so marking aposition at the desired latitude and longitude.

The linkage shown in the embodiment of FIGS. 1 to 3 has an intermediatemember 14 positioned between the component rules 4 and 6. Each componentrule is connected to the intermediate member 14 by a set of threelinkages 16, 18 and 20 or 16′, 18′ and 20′. The linkages are connectedto the component rule 4 or 6 and the intermediate member 14, by pivotpins 22. The pivot pins connecting the linkages 16 and 20 or 16′ and 20′are arranged at the comers of a respective parallelogram so that thedistance between the pivot pins of each link is the same as the other inthe set. Links 16, 16′, 20 and 20′ are the same length as each other.Links 18 and 18′ are the same length as each other and in this exampleas the links 16, 16′, 20 and 20′. The pivot pins 22 are located in thesame relative positions on the component rules 4 and 6. The pivot pinsfor the links 16, 16′, 20 and 20′ are located the same distance apart onthe intermediate member 14, as on the component rules 4 and 6. Ignoringthe links 18, 18′ the component rules 4 and 6 can move relative to theintermediate member 14 whilst retaining the straight edges 8 parallel.The links 18 and 18′ are connected to the intermediate member 14 by acommon pivot pin 22 which is itself slidable in a slot 24, parallel withthe straight edges, in the intermediate member 14. Such constraint ofthe links 18 and 18′ to move together prevents the component rules 4 and6 moving relatively in a longitudinal direction parallel to the straightedges 8 and confines relative movement to a direction normal to thestraight edges.

In an alternative arrangement, the links 18 and 18′ are pivotallyattached to a traveller 19 shown in FIG. 3B. The traveller receives theintermediate member 14 along which it is arranged to slide.

Another linkage which achieves this effect is illustrated in FIG. 4.Here the component rules 4 and 6 are connected by two links 26. Eachlink 26 is pivotally connected to a respective component rule 4 or 6 byone non-sliding pivot pin at 28. Each link is connected to the otherrespective component rule by another pivot pin 30 which is slidable in aslot 32 in the component rule. Each slot 32 is parallel with therelevant straight edge 8. The links 26 are joined between their ends bya further pivot pin 34 such that the distances between the pivot pin 34and the pins 28 and are the same as each other. The pivot pins 28 andthe slots 32 are in the same relative positions on both component rules4 and 6.

In order to facilitate the operation described above, each componentrule 4 and 6 is provided with bosses 40 of relatively low frictionmaterial and at least one area 42 of relatively high friction material.The bosses 40 may be formed integrally of a plastics material, e.g.acrylic or polycarbonate, with the component rules 4 and 6. The bossesare spaced, being placed towards the ends of the component rules. Therelatively high friction areas 42 may be provided, for example by alayer of silicone rubber. The bosses 40 project further from theundersides of the component rules than do the high friction areas. Inuse, to hold a component rule still, as described above, the componentrule is pressed between its bosses so as to flex the component rule tobring the high friction areas to bear against the chart. Placing apencil point in one of the holes 12 to draw the other component ruleacross the chart, as described above, does not flex the component rule,so allowing it to glide across the chart on the bosses 40.

In order to allow a prospective purchaser to see the operation of theparallel rule without the need to unpack it, a package 50 is provided asillustrate in FIG. 6. The package has a card base 52 and a transparentcover 54. The base may be printed with a section of a real or fictitiouschart. The package is wide enough to allow the component rules 4 and 6to be parted and closed. The component rule 4 is provided with a handle56. Similarly, the component rule 6 is provided with a handle 58. Thehandles 56 and 58 facilitate use of the rule as described on a chart. Inthe package, the handle 56 extends into a closed recess 60 to restrainit from moving. The handle 58 extends through an opening 62 allowing itto be accessed from outside the cover 54 so as to separate or close thecomponent rules while the parallel rule remains in the package.

What is claimed is:
 1. A parallel rule comprising two component ruleseach providing one of two opposed parallel straight edges, and a linkageallowing relative movement of the rules in a direction orthogonal to thestraight edges but prohibiting relative movement in a direction parallelto the straight edges, wherein at least one component rule has at leastone through hole suitable to receive the point of a pencil so as to makea line of latitude or longitude on a chart and the other of saidcomponent rules has a through hole in corresponding position to said atleast one through hole of said one component rule.
 2. A parallel rule asclaimed in claim 1, wherein said correspondingly positioned throughholes are disposed along a line in fixed orthogonal relationship withsaid straight edges in all positions of said component rules relative toone another.
 3. A parallel rule as claimed in claim 2, wherein bothcomponent rules have a plurality of through holes spaced along thelengths thereof in corresponding positions and with pairs of said holesbeing in fixed orthogonal alignment with said straight edges.
 4. Aparallel rule as darned in claim 1, the linkage comprises anintermediate member connected to each component rule by a respective setof three links, two links in each set being pivotally connected to boththe intermediate member and the component rule by pivots situated oncorners of a variable parallelogram, the other link in each set beingpivotally connected to the component rule and both pivotally andslidably connected to the intermediate member for sliding movementtogether, parallel to the straight edges.
 5. A parallel rule as claimedin claim 1, wherein the linkage comprises two links each pivotallyconnected to a respective component rule, each pivotally and slidablyconnected to the other component rule for sliding movement parallel toits straight edge and pivotally connected together between the componentrules.
 6. A parallel rule as claimed in claim 1 contained by a package,the package being so formed that at least part of the parallel rule isviable therethrough, and so that the component rules may be opened andclosed.
 7. A parallel rule as claimed in claim 6, wherein the packagehas an opening through which one of the component rules may be accessed,to open and close the component rules, whilst retaining the parallelrule in the package.
 8. A parallel rule as claimed in claim 7, whereineach component rule is provided with a handle, and wherein the packageis so formed as to restrain movement of one handle, the other handleprojecting through the opening.
 9. A parallel rule as in claim 6,wherein the package is at least partly transparent.
 10. A parallel ruleas claimed in claim 1, wherein both component rules are provided ontheir undersides with a pair of spaced bosses with at least one area ofrelatively high friction material, the bosses projecting further fromthe component rules than the high friction areas.
 11. A method of makinga line of latitude or longitude on a chart using a parallel rulecomprising two component rules each providing one of two opposedparallel straight edges, and a linkage allowing relative movement of therules in a direction orthogonal to the straight edges but prohibitingrelative movement in a direction parallel to the straight edges, whereina first of said component rules has at least one through hole suitableto receive the point of a pencil so as to make a line on a chart, themethod comprising aligning the straight edge of the second componentrule with a first line of longitude or latitude at an edge of a chart,placing a pencil point in the through hole in said first component ruleand in contact with said chart, and; while holding said second componentrule still, moving the first component rule and the pencil pointlaterally away from said second component rule for making a second lineon said chart orthogonal to said first line.
 12. A method according toclaim 11, wherein both said component rules have through holes incorresponding positions along the lengths of the rules and with pairs ofcorrespondingly positioned holes being disposed along a line orthogonalto said straight edges; the method further including aligning thestraight edge of said second component rule with said first line at achart edge with a first hole in said second component rule covering aselected mark on said chart and, upon said movement of said firstcomponent rule laterally away from said second component rule, makingsaid second line on said chart along a direction intersecting saidselected mark by means of a pencil point placed in that hole in saidfirst component rule paired with said first hole in said secondcomponent rule.